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Updated May 18, 2015
  Leap second

Image: The leap second, which is added "at that moment" in the world at 23:59:59 UT, 23:59:60 is counted as the above computer screen, the next second is counted 0:00:00 dated tomorrow. Those days, June 30 and December 31 concerned, have a duration of 86,401 seconds instead of the usual 86,400 seconds. Many applications require a still finer precision in particular GPS, fundamental physics applications and applications used in astronomy. Leap seconds can improve the accuracy of geolocation in longitude and land navigation systems as well as interoperability with other existing and future GPS systems (Glonass, Galileo, Beidou, MSAS). But this leap second poses a number of problems because some computer systems are unable to handle leap seconds, its removal is still under study.

A quasar, quasi-stellar astronomical radio source is a galaxy whose core is very energy. Quasars are the most luminous objects in the universe. Specifically, the quasar is the area surrounding a supermassive black hole in the center of a massive galaxy. Quasars are used to measure the rotation of Earth time or the solar day with high accuracy. Un quasar, quasi-stellar astronomical radiosource ou source de rayonnement quasi-stellaire, est une galaxie dont le noyau est très énergétique. Les quasars sont les objets les plus lumineux de l'univers. Plus précisément, le quasar est la région entourant un trou noir supermassif situé au centre d'une galaxie massive. Les quasars permettent de mesurer le temps de rotation de la Terre ou le jour solaire avec une grande précision.

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